Torque transfer devices generally involve two or more shafts interconnected to transfer rotary power (i.e., torque) from a power source to an output. Devices that allow for transfer of torque between two shafts disposed at an angle to one another may be referred to as angular linkages. Such angular linkages include, for example, gear boxes and joints. Gearboxes generally include a first gear rotationally fixed to an input shaft and a second gear rotationally fixed to an output shaft. The first gear and second gear are directly or indirectly linked to form a gear train for transferring torque between the input and output shafts. Gearboxes have a number of desirable attributes, including smoothness of operation and the ability to employ a clutch mechanism to selectively disengage the gears.
Joints typically employ pins to rotationally couple structure associated with an input shaft to structure associated with an output shaft. A variety of joint structures including yokes, balls, intermediate shafts and the like may be employed in this regard. The attributes of joints often include: the ability to withstand high torque environments without slipping; compact, robust and inexpensive construction; and, in some cases, the ability to accommodate varying input shaft/output shaft geometries. Examples of common joint types include universal joints (U-joints) and constant velocity joints (CV joints).
Automobile drive linkages typically involve a number of joints. For example, one or more universal joints may be utilized for transferring power from a transmission to the wheels of an automobile. In this case, the universal joint(s) may allow for the transfer of power between the transmission and the wheels via one or more shafts that are not necessarily linearly aligned. Typically, in addition to transferring power between non-aligned shafts, it is desirable for such universal joints to permit movement between two rotating shafts to accommodate changes in the operating environment. For example, as the suspension of an automobile operates (e.g., compresses or otherwise travels), the angle between two interconnected shafts of a mechanical linkage may change.
Conversely, many other applications exist where rotary power is transferred and while a constant angle is maintained between two or more rotating shafts associated with a joint. For example, the transfer of rotary power between a transmission and the propeller of a motorized boat often is performed at a constant angle that does not change during operation. That is, torque is transferred between first and second shafts that are disposed at a fixed angle relative to one another. In such instances it may still be desirable to utilize a torque transfer device that incorporates a universal joint to transfer power due to the simplicity and/or reduced cost of the device as compared to, for example, a gearbox.
While providing a simplified, cost-effective means to transfer power between rotating shafts, torque transfer devices that utilize universal joints suffer from several problems. For example, two shafts interconnected by a universal joint generally do not rotate at the same speed throughout a rotation cycle when the shafts are at an angle to one another. Though each shaft completes one revolution in the same time as the other shaft, the relative speeds of the two shafts vary during rotation. In this regard, an input shaft driven by a power source may rotate at a constant velocity. However, an output shaft interconnected to the input shaft via a universal joint will, during each rotation, typically rotate faster than the input shaft in four instances, rotate slower than the input shaft in four instances, and rotate at the same velocity as the input shaft in four instances. This can create major problems where shaft speed is high or if the load on the shafts is high. The problem is particularly pronounced where both high speed and high load conditions are present.
In order to alleviate this non-constant rotation of the output shaft relative to the input shaft, an intermediate shaft may be utilized. In this regard, the input and output shafts are interconnected to the intermediate shaft via first and second universal joints. When the input and output shafts are held in a strict geometric relationship (i.e., at equal angles relative to the intermediate shaft and in a common plane), the output shaft rotates at a substantially constant angular velocity relative to the input shaft. In this regard, the intermediate shaft still rotates at a non-constant angular velocity relative to the input shaft, and the output shaft rotates at a non-constant angular velocity relative to the intermediate shaft, but these effects tend to cancel each other out such that the output shaft rotates at a substantially constant angular velocity with the input shaft.
While solving the non-constant velocity rotation problem, utilization of a double joint and an intermediate shaft requires the shafts be supported in a strict geometrical relationship. Furthermore, utilization of dual universal joints and an intermediate shaft results in an enlarged joint and may introduce increased vibration into a system.